In the normal life of a commercially viable oil or gas well it is common for the well to produce water in conjunction with the desired hydrocarbons. In the early stages of production, the flowing pressures are sufficient to carry the undesired water up through the tubing and out of the well to be separated from the hydrocarbons at the surface. After a period of time, as the subterranean reservoir being produced begins to be depleted, the pressures of the reservoir decrease and the rate of the hydrocarbons flow in turn decreases. When this occurs, the flow and pressure decreases have an adverse affect on the capacity of the well to carry and remove the undesired water being produced by the well. This is especially true in natural gas wells. When the well cannot carry co-produced water out of the well bore, it builds up in the production tubing until it literally shuts off flow to the surface. This is commonly known as a dead or drowned well.
In the past, in wells which there has been some production of gas still continuing despite accumulated water, a foaming agent, such as soap or another water-soluble surfactant, has been added to the well, either in liquid or stick form. At present, soap sticks are available in two general types. In the first type, the soap material is a solid and is molded to comprise an elongated rod shaped member which are dropped into the well. The other technique incorporates the use of a water soluble carrier into which the liquid soap material is placed. These soap sticks are bought by the well operator and the gauger drops the sticks into the well. The water in the well dissolves the stick, thereby releasing the soap to create foam.
Such products have been found very efficient in lowering the surface tension of the water and are capable of producing large volumes of foam where the well is producing some gas. The gas entering the well will provide the necessary agitation and gas to transform the now soapy column of fluid into foam, thus lightening the standing column weight and making it easier for the bottom hole pressure to push this now column of foam upward in the well bore and carry the water contained therein to the surface for disposal by conventional methods. This method has been found very effective in removing water from a well while there is still sufficient gas production (i.e., agitation) to effect such foaming. The method just described will not readily produce flow in a well which has been drowned to such a degree that it is not producing a substantial quantity of gas. Although it may eventually produce enough foam to start the liquid flowing from most such wells, the time element involved is in many instances so great as to make it impractical.
Previously, when a well had reached the point where the agitation provided by the well was insufficient to utilize the soap stick process, the operator dealt with the problem mechanically. These methods include a process known as swabbing, which entails literally bailing the undesired water column from the well bore. A plunger is run down the well on a wire line and the water is physically removed. Other alternatives consist of expensive pumping equipment permanently installed in the well. All of such mechanical water removal methods require expensive equipment and considerable time and labor.
U.S. Pat. No. 5,515,924 discloses a technique for reviving water drowned oil and/or gas wells by using a uniformly commingled blend of virtually water free surfactants, foamers and gas generating chemicals manufactured in a solid, cylindrical shape to be dropped down the production tubing. The cylinder of chemicals, upon contact with down hole water, transforms the water into foam, thus lightening the hydrostatic pressure in the well to allow the bottom hole pressure in the well to flow the foam out of the well bore and return the well to commercial production.
U.S. Pat. No. 4,611,664 discloses a technique for delivering liquid chemicals, such as corrosion inhibitors, to the producing zone of the well bore by pouring the chemical into an elongated carrier which is dropped into the well bore. The carrier material is selected so that the liquid chemical contained inside the carrier will dissolve the carrier in the well bore, thereby releasing the chemical into the well formation.
U.S. Pat. No. 5,758,725 discloses a method and apparatus for improving well flow in which a stick of well treating chemical is attached to a plunger for insertion into the well bore. The stick may be either a solid stick of dissolvable well treating chemical, or a dissolvable tube or cylinder containing well treating chemical which will be digested by the chemical after it is inserted into the well bore. Among the chemicals suggested for use with this method are foaming agents for lightening the density of well fluids.
Summary of the Invention The present invention comprises the technique for reviving water drowned or poorly flowing oil and/or gas wells by using a water-soluble carrier to hold liquid soap or other desired foaming agent, or well treating chemicals capable of generating gases upon exposure to water. The water soluble carrier will dissolve in the water standing in the well, releasing the treating chemical. Inside the carrier, there is placed a compressed plug of fabric, plastic or cellular foam. When the tube dissolves, the plug material expands to act as a swab. The soap, foaming agent or other well treating chemical is released above and below the swab, creating bubbles which lighten the standing liquid in the well bore. Formation gas pressure from below the swab will assist in pushing the swab up through the tubing string. The presence of the full bore swab tends to be more effective in displacing a large plug of fluid to the surface than are the prior art methods. The swab is displaced from the tubing string along with the water plug, after which the well will continue to produce until the fluid level again builds up sufficient pressure to block or reduce gas flow, after which the process can be repeated.
The objects and advantages of the invention will be more fully apparent from the following detailed description of a preferred embodiment of the invention and from the accompanying drawings and appended claims.